Two ways to collect them
Lobby racks stock singles you can take today; store.usps.com ships packs of 10 or 25 to your door at no charge. Order a few days ahead, since the packs travel by ordinary post.
The $0.00 aisle
USPS boxes: what's free, what it commits you to
USPS hands out Priority Mail and Priority Mail Express packaging at no charge; the store site listed every box below at $0.00 when we checked on 2026-07-27. The catch sits in the fine print of the branding. A free box locks your parcel into that box's postage, and our live quotes show a plain box on a cheaper service beating it more often than people expect.
Catalog from store.usps.comLive quotes, same dayNo account needed to buy labels
Catalog, then consequences
Sizes below come from usps.com and the postal store; the money columns come from quotes we ran on 2026-07-27.
The free packaging catalog, measured
Dimensions here are pulled from usps.com and the store.usps.com box listings, retrieved 2026-07-27. Everything in this table costs $0.00 to obtain, in lobby racks or shipped to you in packs. What differs is the postage each one obligates.
| Packaging | Outside size | Box cost | Ships as |
|---|---|---|---|
| Small Flat Rate Box | 8-11/16 × 5-7/16 × 1-3/4 in | $0.00 | Flat rate, $13.65 counter |
| Medium Flat Rate Box (top load) | 11-1/4 × 8-3/4 × 6 in | $0.00 | Flat rate, $24.80 counter |
| Medium Flat Rate Box (side load) | 14 × 12 × 3-1/2 in | $0.00 | Flat rate, $24.80 counter |
| Large Flat Rate Box | 12-1/4 × 12 × 6 in | $0.00 | Flat rate, $34.00 counter |
| Flat rate envelopes (five styles) | up to 15 × 9.5 in | $0.00 | Flat rate, from $12.90 counter |
| Priority Mail Small Box | 9-7/16 × 6-7/16 × 2-3/16 in | $0.00 | Priority Mail, by weight and zone |
| Priority Mail Large Box | 12-1/4 × 12 × 8-1/2 in | $0.00 | Priority Mail, by weight and zone |
| Priority Mail Side-Loading Large Box | 15 × 12 × 3-1/8 in | $0.00 | Priority Mail, by weight and zone |
| Priority Mail Express Side-Loading Medium | 15 × 12 × 3-1/8 in | $0.00 | Priority Mail Express |
| Priority Mail Tyvek Envelope | pack of 10 | $0.00 | Priority Mail, by weight and zone |
Your own box against the free one, quoted 2026-07-27
These are checkout totals from our calculator for unbranded boxes, Newark, NJ (07102) to Atlanta, GA (30303) and Los Angeles (90011) to New York (10001), with SMKlog's margin already inside each figure.
| Plain box | Lane | Cheapest live quote | Priority Mail quote |
|---|---|---|---|
| 1 lb, about 10 × 8 × 4 in | Newark → Atlanta | $9.91 USPS Ground Advantage | $14.49 |
| 2 lb, about 12 × 10 × 6 in | Newark → Atlanta | $8.48 USPS Ground Advantage | not in top five that day |
| 3 lb, about 12 × 10 × 6 in | Los Angeles → New York | $11.04 USPS Ground Advantage | $22.34 |
| 5 lb, about 14 × 12 × 6 in | Newark → Atlanta | $13.65 UPS Ground Saver | not in top five that day |
The pattern is blunt. A scrounged box from a closet plus a slow ground service undercut the free-packaging route at every weight we tried, as long as a week of transit was acceptable. Where free boxes shine is the reverse case: you need Priority speed anyway, own no packaging, and the contents fit a listed size. Then the cardboard genuinely is a gift.
The branding is a contract
Print a cheaper label and drop it in a Priority Mail box, and you invite delays or postage-due headaches. Match the box to the service, or use plain cardboard and keep every option open.
Flat rate is its own decision
Four of the free boxes carry fixed nationwide prices, a separate math problem from weight-based Priority. Our flat rate box price guide walks that ladder tier by tier.
Free box questions, answered
Are USPS boxes really free?
The Priority Mail and Priority Mail Express packaging is. Checked 2026-07-27, store.usps.com lists these boxes and envelopes at $0.00 in packs of 10 or 25, and Post Office lobbies stock them loose. The cardboard costs nothing; the postage tier it commits you to is where the money moves.
Which USPS box sizes come free?
The flat rate family (small, two medium shapes, large, plus five envelope styles) and several weight-rated Priority boxes: a 9-7/16 x 6-7/16 x 2-3/16 in small, a 12-1/4 x 12 x 8-1/2 in large, a 15 x 12 x 3-1/8 in side-loader, and a matching Priority Mail Express medium. Sizes are as listed on store.usps.com and usps.com on 2026-07-27.
Can a free Priority box ship Ground Advantage?
No, the branding ties each box to the service printed on it. Ground Advantage needs your own plain packaging, and that is often the better deal anyway; a 2 lb parcel in an unbranded box quoted $8.48 from Newark to Atlanta on 2026-07-27.
Is shipping in a free box cheaper overall?
Frequently the opposite. Free packaging rides Priority Mail, which quoted $14.49 for 1 lb from Newark to Atlanta on 2026-07-27, while the same weight in our own box went for $9.91 on Ground Advantage. Free cardboard paired with pricier postage can lose to a scavenged box on a cheaper service.